1. Field of the Invention
The present invention relates to a headrest for use on a vehicle seat, which is of a vertically movable type being capable of its height adjustment, and in particular to a headrest device of that type having a lock mechanism provided therein.
2. Description of Prior Art
Most of headrests mounted on vehicle seats are capable of its height adjustment. Hitherto, this height adjustable type of headrest is mounted via vertically extending headrest stays upon the top of a seat back of vehicle seat. According thereto, the headrest body can be slidingly moved in vertical direction and locked to a desired degree of height for supporting a head of seat occupant by means of a lock device.
Referring to FIGS. 2 and 3 in conjunction with FIG. 1, such conventional headrest device will now be described. As shown, the conventional headrest device (HD′) is comprised of a headrest body (H), a pair of first and second headrest stays (1′ in FIG. 3) and (1), a pair of first and second holders (P′) (P), and a lock mechanism (M) provided in the first headrest holder (P). As shown, each of the first and second holders (P′) (P) is basically formed by a head portion (PT) and a vertical support portion (PL) extending continuously from the head portion (PT), with a through-hole (PLh) defined in and through both of the head and vertical support portions (PT) (PL).
The first and second holders (P) (P′) are fixedly attached to the respective two support brackets (B) (B) fixed on the top horizontal portion of a seat back frame (F). The first headrest stay (1′) is formed with a plurality of lock notches (11) and a lowest removal prevention notch (10) in one lateral surface (12′) thereof. The two headrest stays (1′) (1) may be slidably inserted in and through the respective through-holes (PH) of the first and second holders (P) (P′).
The lock mechanism (M) is provided in the head portion (PT) of the first holder (P). Designation (M1) denotes an operation portion of the lock mechanism (M), which is defined in the holder head portion (PT) for locking and unlocking operation to be described later.
As shown in FIG. 2, the head portion (PT) comprises a core member (22) and a cap cover portion (21) which covers the core member (22), excepting the operation portion (M1) of the I lock mechanism (M). As shown, formed in the core member (22) are a vertical through-bore (22H) corresponding to the foregoing through-hole (PH) and a horizontally extending cavity (22H-1). The afore-said lock mechanism (M) comprises a horizontal lock plate portion (20A) having a lock hole (20H) formed therein, a lock operation button portion (20) integrally connected with that horizontal lock plate portion (20A), and a biasing spring (24) wound about a horizontal guide rod portion (23). The horizontal lock plate portion (20A) is slidably inserted in the horizontally extending cavity (22H-1) so as to be movable in a direction transversely of the vertical through-bore (22H). Normally, the horizontal lock plate portion (20A) is biased by the spring (24) in a locking direction toward the right side in the drawings.
As also seen in FIG. 2, the first headrest stay (1′) is slidably inserted in and through the through-bore (22H), lock hole (20H) and through-bore of the holder's vertical support portion (PL). In particular, the lowest removal prevention notch (10) of the headrest stay (1′) is shown to be engaged with the lock hole (20H), thereby locking the stay (1′) or the headrest body (H) to a highest level, while positively preventing the stay (1′) against removal from the holder (P). This locked engagement is ensured by the foregoing biasing force of the spring (24) which efforts to retain the lock plate (20A) in the locking position shown in the FIG. 2 where the lock hole (20H) is positively engaged with the notch (10). Under this locked state, if it is desired to unlock the stay (1′), a user has only to push the operation button portion (20A) in an unlocking diction toward the left side in the drawings. By doing so, the lock hole (20H) is disengaged from the lock notch (10) and displaced to a point coaxially aligned with both through-bores (22H) (PLh), so that both two headrest stays (1) (1′) may be moved vertically through the respective two holders (P′) (P). Hence, the user can move the headrest body (H) as well as the stays (1) (1′) vertically though the holders (P′) (P) and also can adjustably lock them to a desired level by allowing the lock hole (20H) to be engaged with a selected one of the lock notches (11).
The above-described conventional headrest device (HD′), however, has been with such a problem that, as shown in FIG. 3, when the stay (1′) is moved vertically while the lock plate (20) is set in the unlocking position, the edge (20He) of the lock hole (20H) is in a frictional contact with one rectilinear lateral surface portion (12) of the stay (1′), and consequently, an unpleasant friction noise generates from therebetween. This is based on the reason that there is a spacing (22H-2) between the lock plate (20) and the horizontally extending cavity (22H-1), and thus, with movement of the stay (1′) in upward and downward directions (U) (D), the edge portion (at 20He) of the lock hole (20H), which is in frictional contact with the rectilinear lateral surface portion (12) of the stay (1′), is subjected to vibration in the corresponding upward and downward directions (U1) (D1), and further, a constant friction is caused between the edge (20He) and rectilinear lateral surface portion (12), which means no change in friction therebetween and therefore a certain friction noise clearly generates therefrom. In particular, when the stay (1′) moves a relative long distance in either the upward or downward direction, a considerable amount of the friction noise generates.